Electric circuit breaker having an arcing contact with larger pivot notch than parallel movable contacts

ABSTRACT

An electrical circuit breaker or isolator, for switching currents of the order of 100,000 amperes, has for each pole thereof, a respective moving contact assembly comprising a plurality of parallel-connected movable contact arms each carrying a respective movable contact engageable with a fixed contact, said arms being of strip metal resiliently mounted sideby-side and substantially parallel to each other in a carrier, each said arm having a V-shaped notch adjacent one end whereby it locates onto an arcuate surface provided by a fixed hinge contact block to which the carrier is hingedly connected, whereby electrical continuity is provided between the arms and the block by direct contact therebetween. An arcing contact arm present in the assembly has the angle of the V-shaped notch in the arcing contact different from that in the other arms to take account of the larger blow-off force occurring between the arcing contact arm and the arcuate surface.

United States Patent [191 Kidd [451 May 22,1973

[75] Inventor: Alan Lister Kidd, Southport, En-

gland [73] Assignee: Dorman Smith Switchgear Limited,

Preston, PR2 2DQ, England [22] Filed: Sept. 29, 1971 [21] Appl. No.:184,799

[58] Field of Search ..200/l46 R, 166 F, 200/170 A, 170 R; 335/15, 16,195

[56] References Cited UNITED STATES PATENTS 3,402,274 9/1968 Bould..200/l46 R 2,821,594 l/l958 Latour ..335/l95 3,560,683 2/1971 Maier etal.... ..200/146 R 3,041,431 6/1962 Mills ..200/170 A 3,365,561 l/1968Jencks et al. ..200/170 A X FOREIGN PATENTS OR APPLICATIONS 1,552,45211/1968 France ..200/l46 R Primary ExaminerRobert K. Schaefer AssistantExaminer-Robert A. Vanderhye Attorney-Kenwood Ross and Chester E. Flavin [57] ABSTRACT An electrical circuit breaker or isolator, forswitching currents of the order of 100,000 amperes, has for each polethereof, a respective moving contact assembly comprising a plurality ofparallel-connected movable contact arms each carrying a respectivemovable contact engageable with a fixed contact, said arms being ofstrip metal resiliently mounted side-by-side and substantially parallelto each other in a carrier, each said arm having a V-shaped notchadjacent one end whereby it locates onto an arcuate surface provided bya fixed hinge contact block to which the carrier is hingedly connected,whereby electrical continuity is provided between the arms and the blockby direct contact therebetween. An arcing contact arm present in theassembly has the angle of the V-shaped notch in the arcing contactdifferent from that in the other arms to take account of the largerblow-off force occurring between the arcing contact arm and the arcuatesurface.

7 Claims, 4 Drawing Figures PATENTEU HLYZZ I975 SHEET 1 BF 3 mvsuroa;ALAN LISTER moo WwwziQon Mn/167 M ATTORNEYS.

PATENTEL MAY 2 21975 SHEET 3 OF 3 mm 9 mv k @v I Nm mv mm @v QN mm GumQM 1 mm W F Q 2 I I. h n 9 N a OQL m N w x Q if wm mm mm mm 9v mv mm 9mm @w v I av mv mm Gm) \m 9 vVv/ z/ INVENTOR:

ALAN LISTER moo ATTOR NEYS.

ELECTRIC CIRCUIT BREAKER HAVING AN ARCING CONTACT WITH LARGER PIVOTNOTCH THAN PARALLEL MOVABLE CONTACTS This invention concerns electriccircuit breakers and isolators and more particularly contactarrangements thereof.

lt is well known, in relation to electric switchgear, such as circuitbreakers, that a socalled blowoff force occurs at the abutting surfacesof successive conductors, e.g. abutting contacts, when current ispassing therethrough, tending to separate such surfaces, and this forceis proportional to the square of the current passing. Accordingly, withcircuit breakers of large short circuit currant capacity, e.g. of theorder of one hundred thousand peak amperes, provision has to be made tocounteract very substantial blow-off forces to keep the movable contactsthereof properly in engagement with their stationary contacts.

For this reason, as well as others, it is advantageous to provide, foreach pole of such a circuit breaker, a moving contact assemblycomprising a plurality of parallel-connected movable contact arms orfingers each carrying a respective movable contact engageable with afixed contact, so that the current in each pole is split according tothe number of arms. The total blowoff force then arising at the abuttingcontacts for any particular current is reduced in inverse proportion tothe number of such arms, as compared with the case where only a singlecontact arm is present, and consequently the actuating mechanism andstructure of the circuit breaker needs only to apply a substantiallysmaller force to retain the movable contacts in their closed positions,without blow-off occurring. However, the mounting of such pluralparallel-connected movable contact arms or fingers in such an assembly,in itself, involves certain difficulties, particularly in relation tomaking provision for current continuity from a fixed conductor to thearms whilst enabling them to move relative to such fixed conductor sothat their movable contacts can engage with and disengage from the fixedcontacts.

The fixed conductor can, if desired, be formed with slots foraccommodating the ends of respective ones of the contact arms orfingers, with a pivot rod extending through the fixed conductor and theends of the arms or fingers so as to provide hinged connectionstherewith. Such an arrangement involves a considerable number ofmachining operations and is therefore expensive.

lt is also known to provide a fixed conductor in the form of a hingecontact block which has a V-sectioned channel extending transverselythereof, each of the arms or fingers having on one end thereof anarcuate lobe which locates in the channel, so that the arms each contactthe hinge contact block at two opposed locations and are pivotablerelative to such block. In such an arrangement, the hinge contact blockcan, if desired, be made by extrusion, as also may be stock from whichthe movable arms or fingers are made.

In the known moving contact assemblies, it is usual to provide aso-called arcing contact". This contact, which is carried upon its owncontact arm, is arranged so that it disengages from its respective fixedcontact after opening of the contacts of the other arms or fingers ofthe assembly, so that any arcing which may occur upon opening of thecontacts is drawn to such arching contact and burning of the othercontacts is minimized. Accordingly, it will be appreciated that theentire current passing through the contact assembly is momentarilydiverted through the arcing contact arm or finger, upon opening movementof the contact assembly. Therefore, where such an arcing contact arm isformed with an arcuate lobe engaging into a V- sectioned channel in ahinge contact block arrangement, as discussed in the precedingparagraph, the blow-off forces occurring at the contact surfaces betweenthe arcuate lobe of the arcing contact arm and the hinge contact block,upon opening movement of the contact assembly, is substantially higherthan that which occurss between the other contact arms and the hingecontact block when current is passing normally through such othercontact arms. From this, it will be appreciated that in practiceadvantages can arise if provision is made for the possibility that thegeometry of the contact surfaces between the arcing contact arm and thehinge contact block can be different from that of the other contactarms. This, of course, is not readily possible with the above-discussedknown V-sectioned channel and lobe arrangement, and an object of thisinvention is to provide a parallel-connected novable contact armarrangement which is suitable for use in electric circuit breakers or inelectric isolators wherein such difference can be provided if desired,and which enables the contact arms to be produced simply andinexpensively.

With this object in view, the present invention provides an electriccircuit breaker or isolator which has, for the or each pole thereof, arespective moving contact assembly comprising a plurality ofparallelconnected movable contact arms each carrying a respectivemovable contact engageable with a fixed contact, characterized in thatsaid arms are of strip metal resiliently mounted side-by-side andsubstantially parallel to one another in a carrier, each said arm havinga V-shaped notch adjacent one end whereby it locates onto an arcuatesurface provided by a fixed hinge contact block to which the carrier ishingedly connected,

whereby electrical continuity is provided between the arms and the blockby direct contact therebetween.

With such a construction, if an arcing contact arm is present in theassembly, the angle of the .V-shaped notch in such arcing contact armmay be different from that of the other arms, so that the geometrythereof is such as to take into account the fact that the blow-off forceoccuring between the arcing contact arm and the arcuate surface, uponcontact-opening movement of the assembly is considerably higher thanthat occurring between the other contact arms and said surface.

Each movable contact arm is conveniently in the form of a metalpressing, the respective movable contact being secured adjacent theother end thereof, e.g. by high speed brazing which can be effectedwithout softening the contact arms.

In the arrangement of the invention, each of the arms may be mounted inthe carrier by a respective locator spring which is shaped, as discussedin our copending Patent application No. 184,800 to provide a loadingportion which engages one longitudinal edge of the arm and a pair oflimbs extending across the arm one adjacent each side thereof and whichlocates on a cross member, extending transversely of the arms, of thecarrier, adjacent the other longitudinal edge of the arm.

In such arrangement, the locator springs serve yieldingly andresiliently to mount the movable contact arms in the carrier, and thespace between adjacent pairs of the contact arms has one limb of thelocator spring of each of said arms extending therethrough, so thatthese limbs serve effectively to locate the arms relative to oneanother.

As described in our aforementioned copending application, each locatorspring is conveniently substantially rectangular in configuration, withits shorter sides constituting the limbs, one of the longer sides beingthe loading portion of the spring, and the other longer sideincorporating a formation whereby it locates on thev cross member.

Said formation whereby the spring locates on the cross member may be aneye; and such eye can be formed by oppositely-directed hooks provided onthe two ends of a single spring-wire length forming the locator spring.

The said one of the longer sides of the locator spring which providesthe loading portion of the spring is conveniently shaped so that only ashort central portion engages with the respective edge of the respectivecontact arm.

The end of each movable contact arm adjacent which the respectivemovable contact is provided is conveniently shaped to provide aprotrusion beneath which engages a lip of the carrier whereby to limitpossible movement of the arms under the loading of their springs.

The invention will be described further, by way of example, withreference to the accompanying drawings which illustrate a preferredembodiment thereof, as applied to an electric circuit breaker, it beingunderstood that the following description is illustrative, and not[imitative of the scope of the invention.

In the drawings:

FIG. 1 is a cross-section through a preferred embodiment of electriccircuit breaker conforming to the invention showing one contact breakerassembly thereof;

FIG. 2 is a plan view of the contact breaker assembly of FIG. 1;

FIG. 3 is a cross-section on the line 3-3 of FIG. 2; and

FIG. 4 is a cross-section on the line 4-4 of FIG. 2.

The preferred embodiment of the circuit breaker conforming to theinvention is a three pole breaker and comprises a generally, rectangularcasing (indicated generally at moulded from a suitableelectricallyinsulating plastics material the interior of which isdivided by appropriate partitions (not shown) to provide three channels(not shown) each of which accommodates a respective contact assembly1 1. A manual operating mechanism (not shown) of the breaker includes apivoted lever projecting through a top cover of the casing 10 andconnected to the contact assemblies 11 by way of a toggle linkage 12incorporating a member (not shown) which is supported by a pivoted tripbar (not shown) extending transversely across the three channels. Arespective bimetal and electromagnet arrangement (not shown) associatedwith each contact assembly cooperates with the trip bar to pivot thelatter, upon occurrence of a sustained overload (i.e., a sustainedpassage of current in excess of the rated current of the circuitbreaker) or upon occurrence of short circuit conditions (i.e. thepassage of a current substantially in excess of the rated current), torelease its support and permit collapse of the toggle linkage 12 andthereby trip the breaker.

The contact assemblies 11 in each of the three channels aresubstantially identical, and therefore it is only necessary to describeon of them in detail.

Such contact assembly 11 comprises, at one end of the channel, a fixedcontact block 13 having a fixed contact strip 14 secured to its uppersurface so as to extend transversely across the channel. In the otherend of the channel is mounted a hinge contact block 15 whose end 16closest to the fixed contact block 13 has bores 17 at each side thereofeach being about three quarters of an inch long and extendingtransversely of the channel and is shaped on its upper surface toprovide a substantially semi-cylindrical upwardly-directed bearingsurface 18 disposed so that its axis extends transversely of the channelsubstantially concentrically of the bores 17.

The bores accommodate respective hinge pins 19 the ends 20, 21 of whichprotrude from the hinged contact block 15 and serve pivotally toconnect, to said hinge contact block 15, an inverted-U-sectioned orinvertedchannel-sectioned movable contact arm carrier 22, with the ends20, 21 of the rod 19 engaging into apertures 23, 24 in respective sidewalls 25, 26 of said carrier 22.

The carrier 22, which is connected to the toggle linkage 12, serves tocarry a plurality of parallel movable contact arms 27 which, in theclosed condition of the breaker illustrated in FIG. 1, extend from thehinge contact block 15 to just above the fixed contact block 13, so thatmovable contacts 28 carried by each of said arms 27 engage with arespective location on the fixed contact strip 14 on the fixed contactblock 13.

There are 13 of said movable contact arms 27 of which the middle one 27a(see FIG. 4) is an arcing contact arm which is longer than the rest, hasits own movable arcingcontact 29 offset relative to the others, and isspring loaded downwards relative to the carrier 22 by an independenthelical spring 30 set into the carrier 22. Each of such movable contactarms 27 is in the form of a metal pressing, of copper strip, for exampleof approximately three-sixteenths of an inch in thickness, generallyrectangular in configuration, and having the respective movable contact28 secured to one edge thereof, adjacent to one end, e.g. by high speedbrazing. Adjacent to the other end, each such strip has a V- shapednotch 31 cut therein, from the same edge, whereby the arm 27 locates onand makes electrical contact with the bearing surface 18 of the hingecontact block 15. The fact that the movable contacts 28 can be securedto their respective arms 27 by high speed brazing has the advantage thatit can be effected without causing the material of the arm 27 to annealand become soft. Any softening of the movable contact arms 27 is to beavoided, of course, since impacts of substantial force occur in theoperation of the breaker, and this would cause distortion of the arms27.

About midway along the length of the carrier 22 a cross member 32thereof extends transversely across the carrier 22 between the sidewalls 25, 26 thereof at a level below the lower edges of the contactarms 27, which lower edges are, of course, the edges in which theV-shaped notches 31 are provided and on which the fixed contacts 28 aresecured. The arms 27 are mounted in the carrier 22 by way of respectivelocator springs 33 which engage with the upper edges of the respectivecontact arms 27 and locate on the cross member 32.

Each such locator spring 33 (FIGS. 3 and 4) is made from a length ofstrong spring wire bent to a substantially rectangular configuration.One of the longer sides thereof is a loading portion 34 which isslightly bowed along its length and provides a linear middle section 35which abuts against a part of the upper edge of the respective contactarm 27. The two shorter sides of the spring constitute guide limbs 36,37 which extends across the respective contact arm 27, one against eachside of the contact arm 27 and join with the other longitudinal side ofthe spring which is provided with a formation 39 is provided by the endsof the length of wire, which ends are curved to form oppositely directedhooks 40, ill which together form an eye around the cross member 32.

Each said one end of each contact arm 27 is formed with a protrusion 42which engages with a lip 43 on the carrier 22 to limit movement of thearm 27 under the influence of its spring 33.

It will be appreciated that the circuit breaker effectively operates inthe same way as prior known comparable constructions of breaker. Withthe operating handle in the on position, the toggle linkage 12 isextended to press the carriers 22 downwards, so that the movablecontacts 28 all engage the fixed contact strip 14 and are loadedthereagainst by their respective locator springs 33.

The moving contact arms 27 in the contact assembly of each pole serve todivide the current passing in said pole, with the consequent advantageof reduced blowoff force (as already discussed herein) at the contactsso that the force necessary to hold the moving contacts 29 in adequateengagement with the fixed contact strip 14 is substantially less than inthe case where each pole has a smaller number of contact arms 27 andrespective movable contacts 28, and the components of the circuitbreaker can be of lesser dimensions and strength than in the latterinstance.

Upon occurrence of a sustained overload or short circuit (as aboveexplained) the toggle 12 is broken, the carriers 27 are displaced awayfrom the fixed contacts 14 to open the circuits through the circuitbreaker, and the handle is moved to the tripped position.

Because the arms each locate by their respective V- shaped notches 31 onthe bearing surface 18 of the hinge contact block 15, there are twocontact surfaces between each said arm 27 and the bearing surface 18,and blow-off forces acting upon the arm 27 at said contact surfaces areat an angle to one another corresponding to the angle between the sidesof the vees of the notches 31. The horizontal components of such forces,of course, substantially counteract one another. The vertical componentsthereof, however, combine and tend to lift the arm 27 from the bearingsurface 18, and the magnitude thereof is a function of the angle betweenthe sides of the vee of the notch 31. Since the arcing contact arm 27ais subject to substantially greater blow-off forces at its contactsurfaces than the other contact arms 27, the angle of the walls of itsnotch 31 can be made sufficiently greater than that of the other arms 17so that the combined vertical components of the blow-off force tendingto lift such arcing contact arm 27a from the bearing surface 18 eitherapproximates to that which occurs on the other arms 27 or issufficiently small to enable actual lifting of the arm 27a to beresisted by the spring loading of the arm 27a.

Each contact arm 27 has a braid 45 welded thereto adjacent its saidother end and a loop 46 of the braid 45 is attached to the hinge contactblock by means of a screw 47. Screws 47 also fasten a length ofL-section angle iron 48 to the hinge contact block 15. This angle ironhas its longer free ends 49 extending beneath the arms 27. The braid 45diverts some current from the edges of the notches 31 and so reduces theblow-off force at surface 18. The angle iron 48 tends to attract thecontact arms 27 when current is flowing therein and so tends to opposethe blow-off forces. These features enable lower strength spring loadingof the contact arms.

The circuit breaker may be constructed with components of lesserdimensions and/or strength than has hitherto been necessary and also hasother advantages. Thus, the arrangement of springs 33 providing for onelimb 36, 37 thereof alongside each side of the respective contact arm 27achieves proper location of the contact arms 27 relative to one another,so that they lie side-by-side in parallel disposition in a very simpleand convenient manner which is easy to assemble. Furthermore, the formof the contact arm 27 is such that they can be manufactured readily andrelatively inexpensively by simple pressing operations as compared withthe expensive castings or extruded sections which have hitherto beenconventionally employed for movable contact arms.

it is to be understood that the invention is not confined to the precisedetails of the foregoing example, and variations may be made to thesedetails without dcparting from the scope of the invention. Thus, forexample, the contact arrangement 1 l of the invention can be employed inan electrical isolator, the construction being such as to provide twoopposed carriers 22 with their contact arms 27 facing one another toprovide therebetween a gap for accommodating a withdrawable conductorleading, for example, to an electrical component, the arrangement beingsuch that relative movement between the contact arms 27 and theconductor is possible for withdrawing the latter to isolate theelectrical component.

What we claim is:

1. An electric circuit breaker or isolator which has, for the or eachpole thereof, a respective moving contact assembly comprising: aplurality of parallelconnected movable contact arms each carrying arespective movable contact engageable with a fixed contact, the contactarms being of strip metal and being resiliently mounted side-by-side andsubstantially parallel to each other in a carrier, each contact armhaving a V-shaped notch adjacent one end for locating onto an arcuatesurface provided by a fixed hinge contact block to which the carrier ishingedly connected, electrical continuity being provided between thecontact arms and the contact block by direct contact therebetween, oneof the contact arms being an arcing contact arm, the angle of theV-shaped notch therein being different from that of the other arms.

2. A circuit breaker as claimed in claim 1, each of the contact armsbeing mounted in the carrier by a respective locator spring shaped toprovide a loading portion which engages one longitudinal edge of thecontact arm and a pair of limbs extending across the contact arm oneadjacent each side thereof and which locates on a cross member,extending transversely of the arms, of

the carrier, adjacent the other longitudinal edge of the contact arm.

3. A circuit breaker as claimed in claim 2, each locator spring beingsubstantially rectangular in configuration, with its shorter sidesconstituting the limbs, one of spective contact arm. it}.

6. A circuit breaker as claimed in claim 1, a length of L-section angleiron being attached to the hinge contact block and one web thereofextending below the contact arms so that when current is passing throughthe arms a magnetic attractive force is set up tending to draw the armstowards the one web and thus the notches into better contact with thearcuate surface.

7. A circuit breaker as claimed in claim 6, the angle iron beingattached to the hinge block by screws, braid being sandwiched betweenthe other web of the angle iron and the hinge contact block so as alsoto be attached thereto by the screws.

1. An electric circuit breaker or isolator which has, for the or eachpole thereof, a respective moving contact assembly comprising: aplurality of parallel-connected movable contact arms each carrying arespective movable contact engageable with a fixed contact, the contactarms being of strip metal and being resiliently mounted side-by-side andsubstantially parallel to each other in a carrier, each contact armhaving a V-shaped notch adjacent one end for locating onto an arcuatesurface provided by a fixed hinge contact block to which the carrier ishingedly connected, electrical continuity being provided between thecontact arms and the contact block by direct contact therebetween, oneof the contact arms being an arcing contact arm, the angle of theV-shaped notch therein being different from that of the other arms.
 2. Acircuit breaker as claimed in claim 1, each of the contact arms beingmounted in the carrier by a respective locator spring shaped to providea loading portion which engages one longitudinal edge of the contact armand a pair of limbs extending across the contact arm one adjacent eachside thereof and which locates on a cross member, extending transverselyof the arms, of the carrier, adjacent the other longitudinal edge of thecontact arm.
 3. A circuit breaker as claimed in claim 2, each locatorspring being substantially rectangular in configuration, with itsshorter sides constituting the limbs, one of the longer sides being theloading portion of the spring, and the other longer side incorporating aformation whereby it locates on the cross member.
 4. A circuit breakeras claimed in claim 3, the formation being an eye formed byoppositely-directed hooks provided on the two ends of a single springwire length forming the locator spring.
 5. A circuit breaker as claimedin claim 3, the said one longer side being shaped so that only a shortcentral portion engages with the respective edge of the respectivecontact arm.
 6. A circuit breaker as claimed in claim 1, a length ofL-section angle iron being attached to the hinge contact block and oneweb thereof extending below the contact arms so that when current ispassing through the arms a magnetic attractive force is set up tendingto draw the arms towards the one web and thus the notches into bettercontact with the arcuate surface.
 7. A circuit breaker as claimed inclaim 6, the angle iron being attached to the hinge block by screws,braid being sandwiched between the other web of the angle iron and thehinge contact block so as also to be attached thereto by the screws.